


Convince Me

by oncethrown



Category: Shadowhunters (TV)
Genre: Dirty Talk, Incest-Be-Gone, Let's Talk About Consent, M/M, POV Alec, PWP, Sex in the Institute, Smut, Top Magnus, communication is key, talking about sex like grownups
Language: English
Status: Completed
Published: 2016-07-04
Updated: 2016-07-04
Packaged: 2018-07-21 13:26:00
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 4,662
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/7388827
Author URL: https://archiveofourown.org/users/oncethrown/pseuds/oncethrown
Summary: <blockquote class="userstuff">
              <p>When Magnus teases Alec about having sex in the Institute, Alec says no. When Magnus admits that it's a two-hundred-year-old fantasy, Alec says no. </p><p>But when Alec thinks about it a little more, he starts to see the appeal. And, technically, it's not forbidden. And it would be fun to give his boyfriend his well-aged fantasy. </p><p>Alec just needs a little convincing.</p>
            </blockquote>





	Convince Me

**Author's Note:**

> I don't think I've ever written PWP before. Shadowhunters is the gift that keeps on giving.

“Quiet,” Alec hissed again, as Magnus drew his hands down Alec’s bare torso, letting his blood-red painted fingernails catch in the waistband of Alec’s boxers.

“I am speaking in a normal, conversational tone.” Magnus’s smile was wide across his face. “Several feet away from a closed door, made of two-inch thick, solid oak.” He tugged the front Alec’s boxers down over his hipbones. “Surrounded by mortar and stone. You are the only one who can hear me.”

The waist band of his boxers stretched as Alec remained stubbornly rooted against his bed. Magnus made a face, which Alec was reluctant to think of as a pout, at him. 

“I could scream and only you would be able to hear me.”

Alec was very aware that Magnus had talked about sex in the Institute a total of three times. He knew this because he had categorically refused every time. Three months ago, he’d refused with a knot of horror in his stomach when Magnus had just been teasing him, fully clothed and trying to make him blush. A month ago he’d refused with a laugh and a shake of his head when he and Magnus had been lying in bed and Magnus had admitted it was a two-hundred-year-old fantasy. 

And—just a week ago— when Magnus had been inside him, growling in his ear about everywhere he wanted to see him blushing and sweating and moaning, Alec had panted hormone-infused agreements to sex in Magnus’s Paris apartment, on his couch, on the balcony, in the shower, on the kitchen floor, and in a couple of positions that were, frankly, anatomically unlikely. And when Magnus, his voice sibilant and low like it got when he was close, told Alec that he was going to come by the Institute in the middle of the day, bring Alec to his bedroom and bend him over his desk with the Angel watching from the stained glass, Alec had lost it. 

He’d practically screamed his release, barely aware of Magnus coming with him until they’d both stilled and caught their breath between kisses. Once they’d both calmed down and cleaned up, Alec had firmly told Magnus that he could talk about whatever he wanted, but they were still never going to have sex in the Institute. Or on the balcony. 

But Magnus’s ideas had a way of bouncing around inside Alec’s head. His scandalous suggestions somehow became more enticing over time. 

And it wasn’t like no one had ever had sex in an Institute. 

Or like it was forbidden. 

Or like anyone would ever know. 

Magnus gently replaced Alec’s waistband against his stomach and leaned over him, pressing a quick kiss to his lips. “We can stop if you’ve changed your mind.”

Alec didn’t answer at first. He set his hands to the back of Magnus’s neck, running his thumbs up into the short hair at his nape. “I keep wondering if anyone saw us come down here.”

Magnus shrugged. Alec watched the way the movement rippled across the muscles in his shoulders. 

“And if they did?”

Alec looked at Magnus’s shoulder again, rather than his face, as he tried to figure out what he wanted to say. Magnus waited, turned his head and pressed a kiss to Alec’s wrist.

“The door doesn’t lock,” Alec said quietly.

Magnus kissed his wrist again. “That is really rather part of the appeal for me.”

Rolling his eyes, Alec let his hands drop away from Magnus down to his cheap navy blue comforter. 

His room felt so… empty and impersonal compared to Magnus’s. Everything in Magnus’s bedroom was luxurious and expensive and announced, loudly, that Magnus had selected and displayed it with great thought. Magnus’s entire loft was curated. And when Magnus dimmed the lights just so, and pressed Alec back onto his blue satin sheets, Alec felt like part of the collection. Not as a conquest or a curio, but like he was one more precious thing that Magnus had taken care to show off to its greatest potential. 

Magnus lowered his mouth to Alec’s face, kissing his cheek, then his forehead. Alec tilted his chin up so Magnus could catch his lips. 

“I feel weird doing it here,” Alec admitted as Magnus pulled back. 

“It is deliciously forbidden,” replied Magnus, diving in for another kiss. 

Alec set a hand at his chest to stop him and Magnus paused patiently. 

“No. I mean…” Alec huffed out a breath and flung a hand to one side, sort of indicating his small collection of Institute furniture. A banged up dresser that some prior Institute resident had somehow managed to burn so that the bottom corner was entirely black. Black clothes spilling out of dinged up wicker hamper. A roll top desk on which Alec had piled a few books about demons and arrows. They were holding down some loose papers. In the corner of the room was an old fashioned chintz armchair, in an ugly faded green color that didn’t go with anything else in the room, other than the threadbare foot stool that sat in front of it. Magnus’s clothes were draped over it, and they were the only spot of color or elegance in the whole room, other than the stained glass window, with its image of the Angel Raziel holding the Mortal Sword and the Mortal Cup. 

“What?” Magnus whispered. 

“Everything in here is two hundred years old. And not in an antique way just in an old way and, I mean… we barely fit on this bed together. I feel…” Alec huffed. “You’re the fanciest thing in here.”

Magnus pushed against Alec's hand, stealing a quick kiss. “You’re the most beautiful thing in here.”

“I feel stupidly young in here,” Alec finally managed. 

Magnus laughed again. “Also part of the appeal.”

Alec raised his eyebrows warningly. “That I’m young?”

Magnus rolled his eyes, and flopped down on the mattress next to Alec. He was already naked. When he rolled onto his side and moved closer, Alec could feel his boyfriend’s erection pressed against his hip.

The tips of Magnus’s fingers started to skim across his chest, catching and tickling in his chest hair. “Not that you’re young, that you were young here. That you did homework in here, and nursed wounds in here, and maybe practiced your sword angles in here.”

“I always practiced in the gym. Training swords aren’t allowed in the dormitories,” said Alec. That just made Magnus laugh and move closer. 

“I like that this is your space, and you probably never let many people in it. And yet, here I am. With you. Naked.”

Alec sigh and turned his head, so that his chin was pressed to Magnus’s forehead. “I feel like people saw us come down here and are wondering what we’re doing.”

“We’re adults,” Magnus replied. “And we could be doing anything. Attending to some sort of Clave business best discussed in private. Having a cup of tea. Sitting on opposite sides of the room, fully dressed and reading the Bible.”

Alec snorted. “Yeah, I’m sure that’s exactly what everyone thinks we’re doing.” 

Alec was well aware that anyone who had seen them walking down the hallway together had probably thought the same thing people thought when they saw Alec leave the Institute with an overnight bag. It didn’t bother him then, why should it bother him now? 

Because Magnus’s loft was different. It was far away, and totally separate from this world. And in this world, Alec realized, he still felt like he wasn’t allowed. 

“We can stop if you’ve changed your mind,” Magnus repeated. “We could get dressed and go back to my place. Or go out for lunch?”

Alec thought for a moment, which must have gone on longer than he thought, because Magnus stopped moving his hand across Alec’s body and sat up, looking worried. “Alec? It’s fine, we can do whatever you want.”

Alec nodded, looking at the concern in his boyfriend’s face. He knew it was fine. Magnus had never pushed him further than he was willing to go. Alec knew that, if it was what he really wanted, they could get dressed, go get something to eat, and pick up where they left off back at the loft. Far away from judgmental eyes, and doors that didn’t lock, and a whole group of people who were actively against Alec being happy.

That just wasn’t what he really wanted. He wanted to be able to give Magnus his silly fantasy.

“Alec?” Magnus asked again.

Alec put his hand to Magnus’s chest, looking at his own fingers, and the way they looked so familiar against the warlock’s skin. “I want you to convince me,” Alec answered in a low, warm, whisper.

Magnus laughed. “I can most certainly do that.” He brushed Alec’s hand off of his chest and climbed back on top of Alec.

Alec let himself be pushed back against the mattress and tried to melt into the heat of Magnus’s kiss. 

It was a good kiss, warm and loving, and Alec sighed into it happily, wrapping his arms around Magnus’s shoulders and pulling him a little closer. Magnus pushed back against his grip and gave Alec a mischievous smile, slotting his thumb underneath Alec’s chin and pinching it gently. 

Just as Alec was about to ask what Magnus was doing, Magnus forced his head to the side, and held it there, just hard enough to make it exciting. 

Alec stared at his stained glass window, watching the way the mid-day sun made the Angel glow as Magnus moved his lips down Alec’s neck, tracing his way down and back up Alec’s deflect rune. 

“Do you know why I want to have you here?” Magnus asked, his lips brushing the shell of Alec’s ear. 

“Because you’re a shameless exhibitionist with some sort of homework kink?” 

Magnus laughed, ducked down and bit Alec’s neck a little too hard. Alec was surprised at himself when his hips snapped up, pressing against Magnus’s naked body without any interference from his mind at all. 

“No,” Magnus replied. He dug one arm into the space between the small of Alec’s back and the mattress, forcing Alec’s body even closer to his own. “I want to fuck you here, because you can be such a shadowhunter sometimes.” He pressed down harder against Alec, rocking his cock against Alec’s cotton covered dick. “So restrained, so stoic, so locked-up,” —Magnus slotted his hand between their bodies, wrapping his fingers around Alec’s cock with a triumphant grin— “So rigid.”

Alec groaned— much too loudly— at Magnus’s touch. 

“I know,” he managed, as Magnus started to stroke him. The soft, blunted touch was maddening.

“Sometimes that’s hot,” Magnus told him, whispering like it was a secret. “Seeing you like that. Leader of the New York Institute, so prim and responsible. But I love seeing you like that and knowing that if I got you alone it would all fall away. The way it does in my bedroom, when you’re naked on my sheets, spreading your legs for me, begging me to make you feel good.”

“Magnus,” Alec gasped, rocking his hips up into his boyfriend’s hand. “Come on, undress me.”

“Not yet,” Magnus replied. Alec moaned in disappointment, but Magnus kept speaking, barely acknowledging the interruption. “I want to see you like that here. Blushed and sweating and moaning— right here, where you’re supposed to be so dignified all the time.”

Alec only had a second of wondering if Magnus could read his mind before Magnus went on. 

“And the next time you’re laying here alone, I want you to remember how it felt when I was fucking you on this bed.” Magnus punctuated this statement with a quick squeeze of Alec’s cock through his boxers that made Alec jump. “And I want you to remember how good it was, and how hard I came because of you.”

Magnus finally slipped his hand into Alec’s underwear, wrapped around him… and stopped. 

“Mag—”

“Do you ever imagine me here?” Magnus murmured. “In the Institute?”

“Yes,” Alec responded, already breathless.

Magnus hummed in approval, and gently spun his palm around the head of Alec’s cock, just once. He paused, looking down at Alec expectantly. 

Alec loved this, and Magnus knew it. He’d spent his whole life learning to push down his desires and and adhere to what the Clave wanted, and then, sometime around when Jace had come to live with them, he’d found himself learning to push down a whole host of desires that he’d never seen coming. He was unlearning the instinct to ignore what he wanted, but he was unlearning it slowly and leaning heavily on Magnus’s ability to get him to try things just to see if he would like them, Magnus’s insistence that he at least try to ask for the things he wanted, and Magnus’s patience with the fact that Alec was still terrible at it. 

Sometimes Magnus would press Alec down into the couch and whisper sexy things to him until the fact that Magnus wasn’t already inside him felt like some medieval torment. Usually all Magnus asked for in return was a couple breathless repetitions of “Please fuck me.” But sometimes Magnus would stop like he was doing now. Tease like he was doing now. Force Alec to talk to him like he was doing now.

Alec could do it. It just took him more time to warm up to it than it took Magnus. More time to overcome inhibitions and ask for what he wanted. 

The corner of Magnus’s mouth twitched as Alec opened his mouth and tried to think of something to say. The longer it took Alec to think of something, the more of Magnus’s mouth crept up into a smirk. 

“What do we do when you think about me here?” Magnus asked nothing in his voice but warmth and patience. He spun his palm again, making Alec shiver and squirm. 

Alec breathed in and tried to dredge up any fantasy he might have called up recently, some night where he slept here instead of at Magnus’s place. Magnus stroked him again, but his mind stayed a total blank, until finally his head tilted far enough back that his door came into view. 

Unmarried shadowhunters lived in single dormitory style rooms. They were all utilitarian, and all the same. They weren’t designed to be bedrooms, they were designed to be soldier’s sleeping quarters. They didn’t lock because it was unthinkable to steal from a fellow shadowhunter, and because for so much of shadowhunter history it would have been completely inconceivable to use your bedroom the way that Alec was using it now. 

There was some allowance for local culture, but for the most part shadowhunters had always been puritanical in their social mores. The expectations for sex education were still that at some point before your wedding night an older relative would take you said and dole out careful and clinical advice. Alec had endured a very red-faced twenty minutes with his father before his own wedding, which he’d spent being being hugely jealous of the Scandinavian Institutes, where, according to Izzy, who’d heard it from one of the transferred shadowhunters, everyone was given a very thorough manual, and the opportunity to requisition birth control. 

Realistically, in the modern world, the worst that was likely to happen to a pair of unmarried shadowhunters who got caught having sex in their room was a little light teasing and maybe a few snide remarks (or in Jace and Clary’s case a very long, very awkward discussion over a dinner with Jocelyn and Luke).

But this was different. Just because people knew what Alec and Magnus were, just because most of them had seen Alec kiss Magnus at the wedding, and just because Alec tried so fucking hard to walk a line between unapologetic and overt, didn’t mean him being with Magnus here in the Institute was the same as Jace and Clary sneaking around when they thought people wouldn’t notice. 

So when Alec thought about Magnus in the Institute— naked and wrapped around him— he went big. Safe in Alec’s fantasies, he and Magnus had fucked in the middle of the candle-lit library. Magnus had ridden Alec in the raggedy office chair in front of the monitors when Alec was supposed to be on night shift. In Alec’s favorite, Magnus pushed him down onto the training room floor after a long and vicious round of sparring and fucked him right there, still dripping sweat with his hands wrapped and ready for the punching bag. 

But that fantasy had been… repurposed from a Jace fantasy that had never been as much fun as the one starring Magnus and Alec didn’t want to bring it up now.

“Alec,” Magnus said again, bending down to kiss him while he finally stopped teasing and started to stroke Alec in a careful but confident rhythm. “I’m starting to think you’re going to tell me something shocking.”

Alec pressed up into the kiss, slipping his tongue into Magnus’s mouth just to hear Magnus sigh before pulling back. “I’m sorry,” Alec whispered. “I’m… this is kind of my limit for being… you know. Adventurous.”

Magnus brushed the hair back from Alec’s forehead, sat up and wriggled his fingers at the door. Three shimmering blue bars of magic flew toward the door, laying across it horizontally as though they were protecting Alec’s door from some sort of siege. Another complicated hand motion sent a wave of purple out over the whole room. Alec’s walls shimmered for a moment before going back to normal. 

“There,” Magnus said. “The door can’t be opened from the outside and the room is sound proofed.” 

Alec pulled Magnus down into a grateful kiss, only feeling a little silly about it since it wasn’t like anyone had ever just walked into his room before. 

Magnus kissed him back, hard, while Alec reached down to pull off his own underwear. He had the band most of the way down when Magnus took over, pulling Alec’s boxer briefs down his legs and tossing them away. He didn’t break the kiss until he’d finished, finally whispering, “When I think about us in the Institute together,” Magnus stopped, pulled in a breath, and wrapped his hand around Alec’s cock again before starting over. “When I fantasize about you and I in the Institute, it’s exactly like this. Sneaking off after a meeting because neither of us can wait any longer. Stripping out of our clothes as soon as the door closes and falling into bed.”

Alec pressed up into Magnus’s hand and flung his arm out to his ancient, utilitarian nightstand. He pulled open the top drawer, retrieved the small bottle of lube hidden at the back, and tapped it against Magnus’s collarbone. 

With a laugh, Magnus took the bottle out of his hand. “You’re impatient like this when I imagine you too.”

“You’ve been waiting two hundred years to have sex in an Institute,” Alec answered. “I’m just trying to help.”

“I’m a very patient man,” Magnus said, popping open the bottle cap.

Alec snorted. “Liar.”

While it was true that Magnus never pushed, never overstepped a boundary, it was just as true that as soon as he was given permission to cross a line, he leaped gleefully over it, occasionally sprinting right up to the next barrier in the same night. Whether Alec found that thrilling or overwhelming depended on the night. 

Magnus laughed and Alec pulled him back into a kiss. Magnus’s fingertips trailed down Alec’s side, over his shoulder, then his ribs, then his hip. The light touch disappeared for a moment, then came back, slick and cool, between Alec’s legs. Alec sighed, canting his hips up a little to give Magnus a better angle. 

“Yes,” Magnus said. “This is exactly what I imagined.”

“Is it,” Alec started, as Magnus slipped one finger into him. “Is it always like this? A quickie in my room?”

“A quickie,” Magnus scoffed. “My fantasies are a bit more sophisticated and varied than that.”

“Tell me,” Alec whispered, pressing back against Magnus’s hand.

“Oh, you’ll have to give me a moment to pick one,” growled Magnus, working a second finger into Alec. “I have so many fantasies about you to choose from.”

Between his words, his touch, and the precaution of the magic guaranteeing their privacy, Alec was finally starting to relax. The stuttering staccato heat that had been in his body since Magnus swept him back here to his room finally started to smooth out. Alec closed his eyes, focusing on Magnus’s voice and fingers. 

“Maybe it starts as a quickie,” Magnus said. “I’m called in for some small errand and you don’t even know I’m here until you see me. And when you do… you know what you can do to me. You distract me, teasing and flirting until I can’t even hope to finish my work, and then finally, when you know I can’t resist, you bring me back here and pounce.”

Magnus punctuated this with another quick sharp bite at the side of Alec’s neck and a thrust of his fingers. Alec writhed underneath him. 

“And I kiss you and suck you and work you open,” Magnus panted. “And finally, slide into you, and feel you warm and tight around me.”

Alec moaned and bucked up into Magnus. “Yes,” he gasped. “Yes.”

“And you’re trying to make me go faster, harder, and I won’t. You seduced me back to your room, and now you’re going to take exactly what I want to give you.”

Magnus’s voice was low and liquid and Alec could barely stand it. He could feel himself, slick and open. His thighs were shaking on either side of where Magnus was still crouched between them. “Yeah, anything you want,” Alec managed. He brought one knee behind Magnus and nudged him forward. A quiet request. 

Magnus pulled his fingers away and for a moment Alec thought Magnus was going to make him wait again until he saw him scoop up the lube bottle and start to slick his cock. “And then I can’t take teasing you anymore. It’s too much, I want you too badly.”

“Magnus,” Alec panted as he felt the beginnings of the blunt push as Magnus finally entered him.

Magnus stopped talking as he slowly moved into Alec, pressing one of Alec’s hands back into the mattress and slotting their fingers together as he moved. Alec had learned how to do this over the last few months. Learned when he needed to ask Magnus to stop because he needed more time or more lube. Learned how to relax and let this initial press of Magnus’s body into his feel good. But Magnus knew it still took a little concentration. He moved slowly, bottomed out, and waited for Alec to let him know it was okay to keep going.

Alec took advantage of the of the pause this time to breathe deep, and take hold of the fact that he really was in his room, in the Institute, with his boyfriend inside him. A thrill went through him, full of arousal, certainly, but something else. He brought his hands to Magnus’s shoulders, smiled at him, and as Magnus started to thrust, shallow and careful at first, before setting a comfortable rhythm, Alec realized that the other feeling was triumph. The Clave would be absolutely horrified by this, and he didn’t care.

“Then what?” Alec asked breathlessly. “What happens after you stop teasing me?”

“Oh, I fuck you,” Magnus answered matter of factly. “I move into you over and over again, until you’re panting and desperate. Until you’re flushed pink all the way down your body, until you’re moaning with your head thrown back.”

“Yes,” Alec answered, tightening his fingers against Magnus’s skin, and pressing back against him, forcing their hips to move together so that Magnus couldn’t pull back.

“And then there’s a knock at the door,” Magnus hissed, freezing so that when Alec continued to move he pulled away, inadvertently letting Magnus slip out of him. 

“Mmhhnnmm,” Alec whined, reaching down to guide Magnus back into him. Magnus grabbed his wrist to stop him.

“And it’s some sort of emergency,” he whispered. “And I get to watch you pull yourself together and go out and be the leader, and know that you’re just waiting for the time when you can pull me back to your bedroom. Know that you’re desperate to finish what we started.”

Magnus slid back into him and Alec keened with relief, wrapped his arm around the small of Magnus’s back and held him trapped there, so he couldn’t get away, canting his hips up until Magnus gasped and collapsed back down against Alec’s mouth. As hesitant as he had been about sex in the Institute with Magnus, he’d still put a stamina rune on his thigh before Magnus had arrived at the Institute. Alec wasn’t going to do something and not do it right. 

They moved together fluently, confident enough in Magnus’s spell work to be loud, confident enough in what the other liked to make each other loud, until finally, Alec gasped, “I do think about you in the Institute.”

“Tell me,” Magnus demanded. 

And Alec did. While Magnus moved inside him, Alec stuttered out a story— much less elegant and evocative than Magnus’s had been, about Alec, sitting alone in front of the cold light of the Institute monitors, watching the pictures and the instruments, ready for the very, very small chance that there would be any demonic activity outside the institute that night, and seeing Magnus come out of the dark, already undressing. Starting to pull himself out of his own clothes as Magnus approached, and taking him right there on the desk. 

“How outrageously negligent, Alexander!” Magnus crowed but broke off with a gasp when Alec thrust his hips back hard onto Magnus. 

Alec tried to keep going, the words that came into his head being driven out just as quickly by his own oncoming orgasm as they were by his amazement at how every one of his clumsy descriptions made Magnus moan and twitch against him, until finally, at an explanation of how Magnus’s flailing arms would throw one of the monitors off the desk, Magnus cried out. Any attempt at coordination or rhythm or talking was gone as Alec waited for Magnus to come. And Alec barely had time to tease Magus before Magnus was wrapping his hands around Alec’s cock and bringing him over the edge too. 

They lay together, gasping and kissing until Magus pulled out and dropped down next to Alec. Alec allowed Magnus to pull Alec onto his chest, where he could feel the rise and fall of Magnus labored breathing. 

“So,” Magnus said, after a few moments. “Out on the control room desk, huh?”

Alec scoffed. “No. Absolutely not.”

“There are definitely ways to make that happen,” Magnus said, his voice light and musical and teasing. 

“Not if I’m involved,” Alec told him. “You want to fuck a shadowhunter in the middle of the institute, you go find another one. There is a difference between fantasy and reality.”

Magnus let out a theatrical sigh. “I suppose. And there are plenty of other fantasies we haven’t been able to give a try yet. Sex on the balcony comes to mind.”

Alec pushed himself up on his forearms and glared at Magnus. “No.”

Magnus smiled and leaned up to kiss Alec’s scowling mouth. “Okay.” He said, dropped his head back against the dark blue pillow, eyes falling shut.

Alec tried to continue glaring, but his orgasm soaked brain was much more interested in visions of the way Magnus’s hair would glisten silver under the moonlight. How surprisingly comfortable the chaise lounge Magnus had set out on the balcony was. How potentially thrilling the hum of the city beneath them might be. 

“Not yet,” Alec amended.

**Author's Note:**

> If you like my stories, please follow me on Tumblr. I post a bunch of Shadowhunters stuff and its the best place to keep up with my new stories, plus some podcast and podfic stuff I'm working on!
> 
> http://oncethrown.tumblr.com


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